Reducing Scorpion Risk

Matthew D. Terry Ph.D., Entomology

Scorpions are arachnids and, as such, are relatives of spiders, ticks and mites. Dozens of scorpion species are native to Arizona and all possess a stinging gland on the tip of their abdomen. The toxicity of the venom varies greatly between species and shows no correlation with the size of the scorpion, in fact, many of the largest scorpions have venom that only causes minor pain and discomfort at the site of the sting. The good news is that there is only one dangerous scorpion in the United States: the bark scorpion (Centruroides exilicauda). The bad news is that this scorpion’s range includes most of Arizona and it is the most common scorpion found in and around human dwellings in the Phoenix area. All Arizona residents should take measures to avoid bark scorpion stings and know what to do in case they are stung.

Form and Biology

With their large pincer-like pedipalps and abdomens narrowed into long tails with a bulbous stinger at the tip, scorpions are easily recognized. Adult bark scorpions are slender, light brown in color and grow to a little over two inches long as adults, but juveniles can be much smaller. They are nocturnal predators of small arthropods (insects, crustaceans, and other arachnids) and spend their days resting in cool, dark, enclosed areas.

Bark scorpions are most active during the warmer months, and will often wait out the winter months in a protected spot, often with many other scorpions. When conditions are favorable bark scorpions can live for several years. They reproduce throughout the spring, summer and fall and bear live young. As the baby bark scorpions emerge they crawl up onto the dorsal side (back) of the female and remain there until they have grown and gone through at least one molt. The outer shell, or exoskeleton of scorpions contains a compound that fluoresces a bright green color under UV light, so individual scorpions can be easily spotted at night by using a portable flashlight with a “blacklight” bulb. Bark scorpions are excellent climbers and can often be found in trees, particularly those with abundant foliage such as palm trees with untrimmed, dead fronds.

Stings

The severity of bark scorpion stings varies depending on the amount of venom injected, the site of the sting, and the age and health of the victim. Victims report feeling initial sensations of numbness or tingling at the site of the sting followed by sometimes intense muscle pain, both near the site of the sting and in throughout their body. This pain is caused directly by the toxin and by the body’s immune system reacting to the foreign compounds. It lasts up to several days, can vary in intensity over time and is often accompanied by a tingling or numbing sensation. In severe cases there may be systemic symptoms such as fever, respiratory paralysis (trouble breathing) and convulsions. Although very unpleasant these stings are rarely life threatening. If you are stung or experience the symptoms described above you should immediately contact your family physician or call poison control. You will most likely be told to take over-the-counter pain medication and an antihistamine such as Benadryl to help manage the symptoms. If symptoms persist or become severe antivenin is available.

Control Measures

You can reduce the number of scorpions around your home by removing areas that provide suitable shelter for them during the day. Woodpiles, dead brush or even clothing left on the ground can harbor bark scorpions. Cinder block walls also provide ideal sites for resting scorpions. Caulking windows and checking the weather stripping around doors can greatly reduce the number of scorpions that gain entry to your home. Other strategies such as wearing slippers when walking through your home at night and being careful when lifting and moving material that may be attractive to scorpions can help to reduce the chance of a sting. An integrated approach including the methods mentioned above and effective chemical control of scorpions using the right combination and amounts of EPA approved chemicals applied to the proper locations provides the best overall protection from the bark scorpion.

About the author: Matthew Terry is the contributing entomologist for Blue Sky Pest Control. He did his post doctoral work at the University of Arizona and currently continues his research and teaches at the University of Texas in Edinburg. Contact Blue Sky Pest Control at 480-635-8492 if you have additional questions or visit the website at www.www.blueskypest.com.